Contact lens wearers with dryness symptoms exhibit significantly more LWE and LIPCOF, but not increased corneal staining, bulbar hyperaemia or decreased PLBUT. LWE and LIPCOF are significantly correlated: this may reflect their common frictional origin. LIPCOF Sum severity scores appear to be most predictive for symptoms.

The composition of the mucus gel of the tear film reflects the competing needs for transparency, stability, hydration, and protection of the ocular surface. Mucins form the macromolecular scaffolding of this hydrated gel, and glycans decorating these glycoproteins represent a rich source of binding ligands that may both modulate microbial binding and regulate the physicochemical characteristics of the gel. This study compares the structure of O-linked glycans derived from the ocular mucins of three species, to determine whether the ocular surface microenvironment dictates the need for a common pattern of O-linked carbohydrate structures. Ocular mucus aspirates were collected from healthy humans, rabbits and dogs. Mucins were purified using standard protocols. O-glycans were released by hydrazinoloysis and subsequently analysed by a combination of HPLC, exoglycosidase digestions and LC-MS/MS. A total of 12 different O-glycans were identified. In human ocular mucin, the majority were negatively charged and terminated in sialic acid, whilst those from rabbit or dog were mainly neutral and terminated in alpha 1-2 fucose and/or alpha 1-3 N-acetylgalactosamine. The glycans were short: the most common structures being tetra-, tri- or disaccharides. Less elaborate glycan structures are encountered at the ocular surface than at many other mucosal surfaces. Species-specific glycan expression is a feature of ocular surface mucins, and has implications for their defensive properties where different microbial and environmental challenges are encountered.

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Atomic force microscopy (AFM) has been used to investigate the heterogeneity and flexibility of human ocular mucins and their subunits. We have paid particular attention, in terms of theory and experiment, to the problem of inducing the polymers to assume equilibrium conformations at a surface. Mucins deposited from a buffer containing Ni(2+) ions adopt extended conformations on mica akin to those observed for DNA under similar conditions. The heterogeneity of the intracellular native mucins is evident from a histogram of contour lengths, reflecting, in part, the diversity of mucin gene products expressed. Reduction of the native mucin with dithiothreitol, thereby breaking the S==S bonds between cysteine residues, causes a marked reduction in polymer length. These results reflect the modes of transport and assembly of newly synthesized mucins in vivo. By modifying the worm-like chain model for applicability to two dimensions, we have confirmed that under the conditions employed mucin adsorbs to mica in an equilibrated conformation. The determined persistence length of the native mucin, 36 nm, is consistent with that of an extended, flexible polymer; such characteristics will influence the properties of the gels formed in vivo.

Absorption spectroscopy is routinely used to characterise chemical and biological samples. For the state-of-the-art in laser absorption spectroscopy, precision is theoretically limited by shot-noise due to the fundamental Poisson-distribution of photon number in laser radiation. In practice, the shotnoise limit can only be achieved when all other sources of noise are eliminated. Here, we use wavelength-correlated and tuneable photon pairs to demonstrate how absorption spectroscopy can be performed with precision beyond the shot-noise limit and near the ultimate quantum limit by using the optimal probe for absorption measurement-single photons. We present a practically realisable scheme, which we characterise both the precision and accuracy of by measuring the response of a control feature. We demonstrate that the technique can successfully probe liquid samples and using two spectrally similar types of haemoglobin we show that obtaining a given precision in resolution requires fewer heralded single probe photons compared to using an idealised laser.